The invention relates to a semiconductor device for generating electrons comprising a semiconductor body of a semiconductor material having at least one structure for emitting electrons, which structure is adjacent to a main surface of the semiconductor body and in which structure electrons can be generated by applying suitable electric voltages, which electrons emanate from the semiconductor body at the location of an emitting surface region.
The invention also relates to an electron tube provided with such a semiconductor device.
The electron tube can be used as a display tube or a camera tube, but it may also be constructed so as to be suitable for electrolithographic applications or electron microscopy.
A semiconductor device of the type mentioned hereinabove is shown in U.S. Pat. No. 4,303,930 (PHN 9532). In the semiconductor device, which is a so-called "cold cathode", a p-n junction is operated in the reverse direction in such a manner that avalanche multiplication of charge carriers takes place. As a result of this, electrons can receive sufficient energy to exceed the work function. The emanation of the electrons is further stimulated by the presence of accelerating electrodes or gate electrodes and by providing the semiconductor surface, at the location of the emitting surface region, with a work function-reducing material, such as cesium.
Particularly the use of cesium as the work function-reducing material often leads to problems. This can be attributed to the fact that, for example, cesium is sensitive to the presence (in the operating environment) of oxidizing gases (such as water vapor, oxygen, CO.sub.2). In addition, as cesium has a high vapor pressure, it evaporates easily, which may be a drawback in applications where (semiconductor) substrates or preparations are situated in the vicinity of the cathode, as is the case in electron lithography or electron microscopy. In addition, ESD (Electron Stimulated Desorption) occurs; the electrons emitted by the cathode induce desorption of the cesium, in particular from slightly oxidized surfaces. A slight degree of oxidation occurs, for example, during spot-knocking of the electron tube.